1. Field of the Invention
The present invention generally relates to vascular stents and, more particularly, to vascular stents that each include at least one filament formed into a wave-like pattern.
2. Related Application
The present application is a patent application for copending continuation-in-part applications Ser. Nos. 07/858,304, filed Mar. 25, 1992; 07/874,347, filed Apr. 24, 1992; and 07/943,000, filed Sep. 10, 1992, all of which are commonly assigned herewith. This application is primarily related to copending design application Ser. No. 07/723,525, filed Jun. 28, 1991, and commonly assigned herewith. This application is also secondarily related to copending design applications Ser. Nos. 07/847,247, filed Mar. 9, 1992, and 07/929,150, filed Aug. 13, 1992, both of which are commonly assigned herewith.
3. State of the art
A stent is a device that can be placed within the lumen, or interior space, of a tubular structure to provide support and assure patency of a contracted, but otherwise intact, lumen. (Patency, the state of being freely open, is particularly important in the field of angioplasty, which is concerned with the reconstruction of blood vessels.) A stent can be used, for example, to hold a vessel open or to tack back an intimal flap inside a vessel after angioplasty. More generally, however, a stent can be used inside the lumina of any other conduit including arteries, veins, vessels, the biliary tree, the urinary tract, the alimentary tract, the tracheobronchial tree, the genitourinary system, and the cerebral aqueduct. Furthermore, a stent might be used inside the lumina of an animal other than a human.
The most common angioplastic procedure, percutaneous transluminal coronary angioplasty ("PTCA"), is employed for enlarging narrowed arteries near the heart. In a PTCA procedure, a balloon-tip catheter is introduced into an artery and then expanded, with the effect of dilating a constricted coronary artery. After an arterial lumen is dilated by a stent, the catheter tip is deflated and the catheter is removed from the enlarged artery.
There are several problems associated with conventional PTCA procedures. First, nearly one-third of all PTCA patients suffer from restenosis--a chronic regrowth of the obstructive luminal plaque--that generally occurs within six months of the angioplasty. Because most restenosis patients also display signs of deteriorating cardiac status, they frequently must undergo another PTCA or a coronary artery bypass graft surgery. However, those patients that elect to undergo repeated PTCA procedures tend to restenos at an even higher rate than first-time PTCA patients.
A second, and sometimes fatal, complication of coronary angioplasty is abrupt re-closure, a condition where a dilated vessel completely closes within twenty-four hours after an angioplastic procedure. Several factors may contribute to acute closure. Those contributors include tearing of the wall of the vessel, tissue removal from dissection, spasmodic contractions, and thrombotic formation of blood clots in a vessel.
Although a clear link has not been established between acute closure and restenosis, some studies have suggested that nearly fifty percent of all PTCA patients who restenos also show some degree of vessel recoil, or collapse, soon after the procedure. Other studies have linked restenosis to sub-optimal balloon dilation. In any event, it is probably safe to say that any hemodynamic abnormality created by angioplasty can contribute to the thrombus formation and smooth muscle tissue proliferation that result from many unsuccessful procedures. It is important, therefore, to provide vascular stents that minimize hemodynamic disturbances caused by angioplasty.